Electrophysiotherapeutic apparatus



p 1948. R. H. MAXSON ELECTROPHYSIOTHERAPEUTIC APPARATUS Original Filed June 25, 1943 IN V EN T 0 Patented Sept. 7, 1948 2,448,541 ELECTROPHYSIOTHERAPEUTIC APPARATU Rolland H. Maxson, Milton, Wis., assignor to The Bur-dick Corporation, Milton, Win, a corporation of Delaware Original application June 25, 1943, Serial No. 492,251. Divided and this application April 16, 1947, Serial No. 741,789

12 Claims.

The present invention relates to electrophysiotherapeutic apparatus and has for its primary object the provision of new and improved appa-- ratus of this type which will operate satisfactorily and be safe under extreme operating conditions.

The primary object of the present invention is to provide a new and improved diathermy equipment comprising an oscillation generator and condition responsive means for rendering the oscillatlon generator ineffective to supply energy to a patient upon the occurrence of an abnormal condition.

A more specific object of the present invention is to provide a new and improved diathermy equipment comprising an oscillation generator, adjustable coupling means for transferring energy from a generator to a patients circuit, and current responsive means-for rendering the generator ineffective to supply the patients circuit upon occurrence of an overload and wherein said adjustable coupling means is operatively connected to and controls said overload mechanism.

A further object of the present invention is to provide a new and improved diathermy equipment wherein the plate voltage supplied to the various tubes thereof is cut off by an overload mechanism when the plate current in the output circuit exceeds a predetermined value" and, more specifically, wherein the plate voltage is cut off until an adjustable coupling between a pickup coil and the output coil of a plate tank circuit is reduced to a minimum value by a resetting switch. Accordingly, it is necessary that the overload be relieved by reducing the coupling before the plate voltage can be reapplied.

A further object of the present invention is to provide an apparatus of the character specified wherein it is impossible to leave the resetting switch on and thereby cause a periodic application of plate voltage and periodic operation of the overload apparatus under certain conditions which may result from improper adjustment of certain elements of the apparatus.

Further objects and advantages of the present invention will become apparent from the ensuing description, in the course of which reference is had to the single figure of the accompanying drawing illustrating schematically one embodiment of the invention.

In general diathermy equipment of the type to which my invention applies consists of a circuit for producing radio frequency oscillations atpower level together with a means for coupling the patient to the oscillation generator. Commonly, the oscillations are produced at power 2 level by a power oscillator circuit, but under some circumstances, principally in order to facilitate control and avoid interference, it is preferable to use a low level precision master oscillator, the output of which passes through a desired number of-stages of voltage and power amplification.

Since the circuits used for producing oscillations at power level by either of these methods is largely a matter of choice and since both systems are well known, I will use herein, unless otherwise specified, the common generic term oscillation generator" or the equivalent in the sense of circuit means for producing oscillations at power level even though such a circuit may include such common expedients as voltage, insulation, frequency multiplier or power amplifiers.

I have illustrated the present invention in connection with an oscillation generating circuit which uses a low level master oscillator feeding into successive stages of amplification, only the last stage of which is shown in detail since the invention is concerned primarily with overload of the power portion of the circuit and with the portion which couples the patient to the oscillation generator.

In the single figure of the drawing the apparatus is illustrated as comprising, in the main 2. master oscillation generator and amplifier to supplying a final amplifier 12 having a pair of output or patients terminals H. In the embodiment of the invention illustrated, these terminals are adapted to receive an applicator drum or a cable of a type commonly used with high frequency therapeutic apparatus, which has not been illustrated. The apparatus includes, in addition, 'a low voltage power supply unit 16, a high voltage power supply unit l8, a combination filament transformer and voltage adjusting auto transformer 20', and a control unit 22.

The main elements referred to, and also other components to be referred to hereinafter, are all mounted in and upon a suitable portable cabinet which is preferably, but not necessarily, made of metal. amplifying means in may be of suitable construction, although it is preferred that it be of the type disclosed and claimed in my copending application Serial No. 492,251, of which this application is a division. In brief, it may be stated that the master oscillation generator is of the crystal controlled type supplied with power through the conductors 24 from the low voltage power supply It, which includes a transformer 26, and through conductors 28 from the high voltage power supply II, which includes a transformer 30 and a pair The master oscillation generator andof rectifier tubes 32. The high voltage rectifier output appears across a voltage divider resistor 34 to various portions of which the conductors 28 are connected. Power is supplied to the primary windings of transformers 26 and 30 through the conductors 36 and 38 in a manner hereinafter to be described in greater detail.

The tubes of the final amplifier I2, which are operated as class C amplifiers, are preferably of a low impedance type (such as G. E. FP265) and are connected to provide push-pull amplification.

The final amplifier is supplied with high frequency oscillations through a radio frequency transmission line 40 of the concentric cable type. The transmission line terminates in a coil 42 inductively coupled to a center tapped coil 44 forming part of a grid tank circuit including also a dual section variable air spaced capacitor 46, the center plate of which is connected to the chassis. The terminals of the tank circuit are connected by conductors 48 and 50 to the grids 52 and 54 of the tubes, which are numbered 56 and 50. The filamentary cathodes and 62 of the tubes are connected in parallel by the conductors 64 which are connected, in turn, by conductors 66 to the secondary winding 68 of the filament transformer 20. A radio frequency bypass condenser is connected across conductors 64 and the separate conductors are connected to the chassis by the radio frequency by-pass condensers I2 and 24. These condensers provide return circuits for the radio frequency grid and plate currents and keep the filaments at ground for radio frequency currents.

Grid bias is supplied to the grids 52 and 54 0f the two tubes by a grid leak resistor l6 connected to one of the conductors a l and to the center tap of coil 44. A D. C. grid current flows through the resistor 16 thereby setting up a direct current voltage providing bias for the grids.

The amplifier I2 includes also a plate tank circuit comprising a two part inductance coil 00, a capacitor 82 of the fixed air spaced type, and a trimmer capacitor 84 also of the air spaced type. The mechanical aspects of the particular capacitor 02 preferred are described and shown in my earlier Patent No. 2,436,114. The plate tank circuit is connected to the anodes 86 and 88 of the tubes 56 and 58 through conductors 00 and 82, respectively. The trimmer condenser 84 is adjusted with the patients circuit coupling coil 94 set for zero coupling. Plate voltage for the two tubes is supplied by a conductor 06 connected to the mid point of inductance coil 80 and having interposed therein a radio frequency choke coil 98. A by-pass condenser I00 serves, together with the coil 98, as a filter to isolate the direct plate current voltage from the radio frequency voltage. The plates of condenser 82 and 84 are connected to each other and by a conductor I02 to the plate voltage supply line 96. Neutralizing condensers I04 and I06 connect grids 52 and 54 to plates 88 and 86, respectively. They minimize self-oscillation and this can be further minimized by shielding and isolation of the external plate and grid circuits.

The patient's circuit is coupled to the output tank circuit of the oscillation generating apparatus by the previously mentioned two turn output coil 94. This coil is connected in series with a pair of variable air spaced tuning capacitors I08 and H0 which are interposed between the terminals I4 and the opposite terminals of the pickup coil. These capacitors are adapted to be adjusted to tune the patient's circuit into resonance with the plate tank circuit. The capacitors are mounted on a common shaft and are adjustable, as by means of a manually operable control knob II2 suitably connected to the shaft as through reduction gearing to provide an accurate control.

The amount of energy transferred to the patient may be varied by adjusting the coupling between the pickup coil 94 and the coil of the plate tank circuit. This adjustment is preferably effected by rotary movement of a support II4 upon which the pickup coil may be suitably mounted. This support is preferably made of insulating material and it may be rotated in some suitablemanner (not shown) by rotation of a manually operable knob II5 or other device having an indicating pointer and operatively connected to the support II4. While it is preferred that the coupling of the coil 94 with the coil 80 be adjusted by rotating the coil 94, there are other and effective means of adjustably coupling the coils. For example, it is within the skill of one versed in the electronic transmitter art to mount the coils for rectilinear axial or transverse movement relative to each other, and the specific means chosen to effect the adjustable coupling is immaterial.

The power supply transformers 26 and 30 are supplied with energy from the auto transformer winding I20 of the transformer 20, as heretofore indicated, through conductors 36 and 38 upon closure of a switch H0 hereinafter to be called the oscillator switch. Conductor 36 is connected to an output tap II8 on the auto transformer winding I20, whereas the conductor 38 is adapted to be connected to the lower terminal of the winding upon closure of switch I I6, the closure of which, however, will not complete the energizing circuit unless a main switch I22 has been closed for a certain length of time and unless a condition responsive switch I24 is also closed.

Power is supplied to the transformer 20 from a suitable alternating current source, which may be connected to the terminals I26 of a plug type connector. The supply of power to the winding I20 is under the control of the main switch I22, illustrated diagrammatically as a simple knife switch (but which is preferably a circuit breaker type of switch capable of opening under predetermined overload conditions). One terminal of the winding I20 (the lower one) is connected to one of the terminals I26 through a radio frequency choke coil I28 constituting, with capacitor I30, a power line filter. The other terminal of winding I20 is shown connected by conductor I32 and a rotatable voltage adjuster arm I34 to the other terminal I26 through the switch I22, conductor I36 and a radio frequency choke coil I38 constituting, with capacitor I40, a second power line filter. Adjacent terminals of capacitors I30 and I40 are connected to a third plug terminal I42 by conductor I44. Terminal I42 is also connected to the cabinet and chassis and is adapted to be connected to a good ground, such as a water pipe.

The voltage adjusting arm I34 is provided so that the apparatus may be operated at designed voltage irrespective of line voltage. To enable the operator to ascertain that the proper adjustment has been made, there is provided a voltmeter I46 supplied with energy from the filament secondary winding 60 through conductors 66. Twelve voltage adjustments are obtainable, each constituted by connection from a fixed contact associated with the movable contact arm I34 and connected to a suitable tap on the transformer winding I20. Only three of these connections are shown-the first, middle and last-the others being omitted for the sake of clarity of disclosure. A pilot light I46 is connected across two contacts of the voltage adjuster and thereby across a small fraction of the winding I20 in order to provide an indication of the energization of the winding I20.

The circuit for energizing the primary of the auto transformer winding I20 is as follows: right line terminal I26, filter coil I36, conductor I26, main switch I22, voltage selector contact arm I64, conductor I 32 to one of the twelve input taps at or near the upper end of the winding I20, transformer winding I20, lower terminal of winding I26, filter coil I26 and left line terminal I26.

The closure of the main power switch I22 energizes a time delay relay conditioning the power supply means for operation after a time interval and upon closure of the oscillator switch H6. The time delay is provided by a thermal time delay relay including a coil I50, a resistance heater I52 energizable upon closure of the main switch I22 and three movable switch blades I54, I56 and I56, of which the last two mentioned are operable by the coil. The switch blade I54 is a bimetallic one adapted, when heated by resistance heater I52, to move to the right and close an energizing circuit through coil I50, preferably after a delay of about fifteen seconds. Resistance heater I62 is energized immediately upon the closure of switch I22 through a circuit including the right line terminal I26, filter coil I36, conductor I66, switch I22, conductor I60, connected to the heater, conductor I62, the movable switch blade I56 in engagement with contact I64, and conductor I66 leading to the filter I26 and left terminal I26. The energizing circuit for coil I 50 closed by the bimetallic switch blade I54 is the same as that for the heater circuit to conductor I60, which is also connected to coil I50, the circuit from the coil I50 to the other power terminal being completed through switch blade I54 and conductor I66. When coil I50 is energized, it completes a holding circuit for itself through conductor I68 and switch blade I56 in its operated position. The heater I52 has its circuit broken and is deenergized by movement of switch blade I56 to its operated position.

When oscillator switch H6 is closed after operation of relay I50, conductor 38 is electrically connected to the lower terminal of transformer winding I20, with the result that the primary windings or transformers 26 and 30 are energized because the other terminals of these two windings are connected to winding I20 through conductor 66. Conductor 38 is connected to winding I20 through a circuit including oscillator switch II6, conductor I10, switch blade I 12 of the overload mechanism which includes the previously referred to switch blade I24, conductor I14, switch blade I16 of the time delay relay, movable switch blade I56 in contact with it, and conductor I66 which is connected to the lower terminal of the transformer winding I20. It is apparent, therefore, that the closure of the oscillator switch II6 will not render the power supply units operative unless the main power switch I22 has been closed to energize transformer 20 for a short period of time.

The complete circuit to energize the transformers 26 and 60 from the secondary of the auto transformer winding I20 is as follows: winding I20, output tap II6, conductor 66, parallel pri- 6 l mary windings of the transformers 26 and 66, conductor 66, oscillator switch II6, conductor I16, contact I12, movable switch blade I24, conductor I14, contact I16, movable blade I56, conductor I 66 and lower terminal of the auto transformer winding I20.

In accordance with the main feature of the present invention, the apparatus is adapted to be rendered inoperative or ineffective to supply energy to the patients circuit upon the occurrence of an abnormal condition in the oscillation generator such as an overload. In the event of an overload, i. e., when the plate current of tubes 56 and 56 rises to some predetermined maximum value. the apparatus is rendered inoperative in suitable manner as by cutting off the plate voltage until the relay mechanism is reset, which is accomplished by manually adjusting the coupling between the pickup coil 64 'and the tank coil 66 to a minimum value such as the zero point of the power control I I5 or preferably slightly below this point. Accordingly, the plate voltage cannot be restored to render the apparatus operative until the coupling has been reduced to a point below which the overload no longer exists.

The overload mechanism includes an overload relay coil I60 connected in the plate cathode circuit of the output tubes 56 and 56. More specifically, the relay coil is in circuit between a common conductor I62 of the power supply and the filament transformer winding 66 connected to the cathodes 60 and 62 of the tubes. The circuit from the coil I60 to the transformer winding 66 includes conductor I64 and the circuit from the transformer winding 66 to the cathodes includes the conductors 66. The circuit from coil I60 to the plates of the tubes includes the conductor I66 leading to the'common conductor of the power supply. The coil I60 also has associated with it a low frequency filter constituted by a low frequency choke coil I66 connected in series with it and a by-pass capacitor I60 connected in shunt with it. This filter smooths the pulsating direct current flowing in the plate circuits of tubes 56 and 66, thereby preventing chattering of the relay. The value of current at which the relay operates is adjustable by resistor I62, also connected in shunt with the coil I60. The plate current of the tubes is measured by a direct current milliammeter I64 interposed in conductor I64, which is also used as an output meter to enable the operator to judge relative dosage.

The overload relay operates the previously mentioned switch I24 so that when the latter is moved out of engagement with contact I12 the energizing circuit to the transformers 26 and I6 is broken. In the illustrated embodiment the switch I24 is also latched when thus operated by a spring biased latch I66.

In order to reset the switch I24, it is necessary manually to adjust the coupling to a minimum which is slightly below the "zero point. When this is done the latch is retracted by a solenoid I66, the energizing circuit for which can be closed through a pair of contacts 200 associated with the pickup coil support II4. These contacts are so arranged that they can be closed by a cam 20I secured to rotate with the support II4 only when the pick coil 64 is held slightly beyond th zero setting. At this time the solenoid I66 is energized from winding I 20 of transformer 20 through the following circuit: output tap I I6, conductor 66, the contacts 200, conductor 202, solenoid I66, conductor 204, switch contact 206, movable switch blade I24 in engagement with the latter, con- 4 7 ductor I14, switch blade I58 in engagement with contact I18, conductor I86 and the terminal at the lower end ofthe winding am. When the solenoid I98 is energized, the latch I96 is retracted topermit'the/return of switch blade I24 to..its vindicated position (to which it may be spring biased) to engage contact I12.

. structed and arranged that the contacts are not closed except when the support is manually adjusted to move the pickup coil slightly beyond a zero coupling position and against the pressure of a spring 208. Immediately the support l M is released, as by releasing the power control knob lib the'sprlng gill? returns the coil support M4 and coil 9% to their zero position thereby permitting contacts 2% to separate. A cooling blower tile is adapted to be energized simultaneously with the energization of transformer 2t by connection thereof across the secondary of the auto transformer winding lid by means of the conductors 3t and lot.

- The transformer 255 includes a number of filament secondary windings 2112, 206, 206 and 201i, while the transformer ibincludes a secondary winding 22d connected to a signal light 222 through wnduotors 222%.

In operation, either a cable or drum or other type applicator is connected to the output termirials l8- and this is done in accordance with conventional modes of application of these devices. The main switch 622 is then closed with the result that transformer 2t) and blower iii are energined. Energization of the transformer is indicated by the pilot light M8. The transformer immediately supplies power to the filaments of all the tubes including those of the power supply units 58 and it, thereby conditioning them for operation. At the same time, volt meter Hit indicates the voltage appearing across the transformer winding til. In the event of line voltage changes, the voltage adjuster lii l may have to be adjusted. This adjustment is also usually necessary when treatment is stanted because of line voltage drop. Closure of the main power switch l22 also efiects energization of resistance heater E52 and energization of coil I50, afterj5 a time interval, through bimetallic switch (blade is, so that transformers 28 and 30 of the two power supply units may thereafter be energized upon closure of oscillator switch l I 8. The oscillation generating apparatus is thereby rendered operative and this is indicated by the lamp 222 which is supplied with power from transformer 2!. Full operation of the device is also indicated by the reading of the milllamlmeter 4, which it may be remembered indicates the plate current in the output stage.

' With the apparatus in full operation the next step is the adjustment of the resonance control M2 to tune the patients circuit into resonance with the plate tank circuit of the output stage. ,This is done with the power control H5 adlusted to one of its minimum coupling positions. The resonance control should always be adjusted to give maximum plate current, the indication of resonance. Adjustment of control knob M2,

' of the adjustment depends upon the particular application given to the patient.

The energy transferred to the patient is controlled by the power control H5, which adjusts the coupling between the pickup coil 94 and the inductance coil 80. dl-cated by the plate current milliammeter I84. Should the control be turned too high, :1. e., to couple too closely the circuits. then under certain. conditions the overload relay I80 may be energized suflicient'ly to operate the switch I24 from its indicated position into engagement with contact 208. This, as heretofore described in detail, results in the deenerglzaltion of transformers 26 and 30 and in the termination of the supply of voltage to oscillation generating apparatus whereby the latter is rendered inoperative or ineffective to supply energy to the patient. The apparatus can be restored to operative condition only by adjusting the power control Hi to a minimum coupling position, in which it has to be held and from which it is returned to "zero coupling position by the spring 208 acting upon the pickup coil support M l. Such turning of the power control results in the energization of reset solenoid Hill which withdraws latch tilt to enable switch blade I2 3 to move to its indicated position.

The operation of the overload mechanism is indicated by (the pilot light 222. it is supplied with energy from. transformer winding 2% so that it is lighted whenever oscillator switch M6 is closed and the apparatus is in operation. Should the overload mechanism operate with the switch i it closed, then the transformer winding 2% is deenergized and the light 222 extinguished. Thus the extinguishment of the light with the oscillator switch closed indicates operation of the overload mechanism.

While there has been described but a single preferred embodiment of my invention, many modifications may be made without departing from the spirit of the invention, as indicated herein and otherwise, and I do not wish to be limited to the precise details of construction set forth, but desire to avail myself of all changes within the scope of the appended claims.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States, is:

1. An electrotherapeutic apparatus of the type comprising an oscillation generator having a resonant circuit including an inductance coil, and a patients circuit, including an adjustable coupling means :between the generator and the patient's circuit and including a coupling coil in said patients circuit coupled to said inductance coil, means for adjusting the position of said coupling coil relative to the inductance coll for controlling the transfer of energy to the patients circuit, an overload mechanism connected to be responsive to an overload condition in the oscil- The energy transfer is in-" the oscillation generator to the patients circuit,

' an overload mechanism connected to be responsive to an overload condition in the oscillation generator and operable to cut oflf the supply of energy to the patients circuit upon occurrence of such an overload, and means operable to reset the overload mechanism upon adjustment of said coupling means to reduce the transfer of energy.

3. An electrotherapeutic apparatus of the type comprising an oscillation generator and a patients circuit, including adjustable coupling means for controlling the transfer of energy from the oscillation generator to the patients circuit, an overload mechanism connected to be responsive to an overload condition'in the oscillation generator and including a coil and a switch operable thereby to cut off the supply of energy to the patients circuit upon occurrence of such an overload, and means including a latch holding said switch in its operated position for temporarily preventing resetting of the overload mechanism after operation thereof, and means operable in response to adjustment of said coupling means to unlatch said switch and reset the overload mechanism.

4. An electrotherapeutic apparatus of the type comprising an oscillation generator and a patients circuit, including adjustable coupling means operable between a minimum coupling position and other positions for controlling the transfer of energy from the oscillation generator to the patients circuit, an overload mechanism connected to be responsive to an overload condition in the oscillation generator and operable to cut off the supply of energy to the patients circuit upon occurrence of such an overload, and means to prevent resetting of the overload mechanism after operation thereof unless the coupling is reduced to said minimum coupling position.

5. An electrotherapeutic apparatus of the type comprising an oscillation generator and a patients circuit, including adjustable coupling means for controlling the transfer of energy from the oscillation generator to the patients circuit, said coupling means being operable to vary the coupling between a minimum value and other values and being also operable beyond said minimum value position, an overload mechanism connected to be responsive to an overload condition in the oscillation generator and operable to cut off the supply of energy to the patients circuit upon occurrence of such an overload, means to prevent resetting of the overload mechanism after the operation thereof unless the coupling is reduced beyond said minimum value position, and means acting upon said adjustable means tending to return it from beyond said minimum value position to said minimum value position.

6. An electrotherapeutic apparatus of the type comprising an oscillation generator and a patients circuit, including coupling means adjustable between minimum and other coupling positions for transferring energy from the oscillation generator to the patients circuit, means for adjusting said coupling means, an overload mechanism connected to be responsive to an overload condition in the oscillation generator and operable to cut off the supply of energy to the patients circuit upon occurrence of such an overload, and means operable by said adjusting means to reset the overload mechanism when said adjusting means is adjusted to substantially the minimum coupling position.

7. An electrotherapeutic apparatus of the type comprising an oscillation generator and a pa tients circuit, including coupling means for transferring energy from the oscillation generator to the patients circuit, manually operable means for adjusting said coupling means, said means being operable from a minimum operative coupling position to other positions and also beyond said minimum coupling position, an overload mechanism connected to be responsive to an overload condition in the oscillation generator and operable to cut oil the supply of energy to the patients circuit upon occurrence of such an overload, means operable by said adjusting means to reset the overload mechanism when said adjusting means is moved beyond said minimum coupling position, and means for automatically returning said adjusting means to said minimum coupling position when said adjusting means is released.

8. An electrotherapeutic apparatus of the type comprising an oscillation generator and a patients circuit, including coupling means for transferring energy from the oscillation generator to the patients circuit, means including a first switch for conditioning said generator for operation and a second switch and a circuit controlled thereby for rendering said generator operative, time delay means associated with said last mentioned means for providing a time interval after the conditioning before said generator is rendered operative, means for adjusting said coupling means, an overload mechanism including a switch in said circuit operable to render the oscillation generator inoperative and thereby cut off the supply of energy to the patients circuit upon occurrence of an overload in the oscillation generator, and means controlled by said adjusting means for reclosing said switch to reset the overload mechanism and thereby to render said generator operative.

9. An electrotherapeutic apparatus comprising an oscillation generating means, adjustable coupling means for transferring energy from said oscillation generating means, manually operable means operatively connected to said coupling means for adjusting the same, electrical condition responsive means coupled to said oscillation generating means and controlling the operation of said generating means, said condition responsive means being operable to render said generating means inoperative in the event of abnormality in said condition, and means operatively connecting said adjusting means and condition responsive means and operable by said adjusting means in a reduced coupling position to condition said condition responsive means for resetting.

10. An electrotherapeutic apparatus comprising an oscillation generating means, adjustable coupling means for transferring energy from said oscillation generating means, manually operable means operatively connected to said coupling means for adjusting the same, electrical condition responsive means coupled to said oscillation generating means and controlling the operation of said generating means, said condition responsive means being operable to render said generating means inoperative in the event of an abnormality in said condition, means operatively connecting said adjusting means and condition responsive means and operable by said adjusting means in a reduced coupling position to condition said condition responsive means for resetting, and means operably associated with said condition responsive means for resetting it when it is thus conditioned.

1 A electrotherapeutic apparatus comprising an oscillation generating means, adjustable coupling means for transferring energy from said oscillation generating means, manually operable means operatively connected to said coupling means for adjusting the same, overload responsive means coupled to said oscillation generating means and controlling the operation of said generating means, said overload responsive means being operable to render said generating means inoperative in the event of an overload in said oscillation generating means, electric circuit means including a set of contacts effective to reset said overload responsive means upon actuation of said contacts, and means operated by said manually operable means for actuating said contacts when said manually operable means is operated to adjust said coupling means to reduced coupling position.

12. An electrotherapeutic apparatus comprising an oscillation generating means having a power supply means and an output tank circuit including a stationary coil, adjustable coupling means comprising a movable co'l associated with said stationary coil for transferring energy from said oscillation generating means, manually Operable 25 2,066,522

means operatively connected to said movable coil for moving it to adjust the coupling, overload responsive means including a winding in said power supply means, means including a switch controlling said power supply means to said generating means openable by said overload responsive means upon occurrence of an overload to cut off the power supply to said generating means and thus to render it inoperative in the event of an overload, and means including switch means operable by said adjusting means in reduced coupling position to condition said overload responsive operated switch for closing, and means for closing said switch to supply power to said oscillation generating means.

HOLLAND H. MAXSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 7 Date Number Name 1,645,215 Bauer Oct. 11, 1927 Doherty Jan. 5, i937 Certificate off i'forreeticn Patent No. 2,448,5ii.

September 7, 1948.

ROLLAND H. MAXSON It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as'follows: Column 5, line 55, for or transformers read of transformers; column 6, line 69, for pick coil read pickup coil; column 7, line 24, for position read positions; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 16th day of November, A. D, 1948.

THOMAS F. MURPHY,

Assistant @ommissioaer of Patents. 

